Pain caused by nerve injury accompanies a wide variety of conditions such as trauma, surgical incision and amputation, inflammation, HIV/AIDS and cancer, and is inadequately treated by currently available methods. Primary sensory neurons, including their somata in the dorsal root ganglia (DRG), are critical sites of pathology, yet their potential as a therapeutic target has not been pursued. We have previously shown peripheral nerve injury causes loss of inward Ca2+ flux (ICa) that elevates sensory neuron firing and contributes to neuropathic pain behavior in rats. The currently proposed research will extend these findings. Specifically, our FIRST AIM is to examine the novel theory that nerve injury causes hyperalgesia by depressing the activity of CaMKII, a molecular decoder of neuronal frequency information. Ca2+ channels admit a diminished inward flux of Ca2+ as pCaMKII diminishes. We have established a strong link between low ICa and increased excitability. Thus, neuronal activation after injury results in a greater burst of afferent impulses and an amplified pain experience. Accordingly, we will test this overall hypothesis by quantifying CaMKII protein and function after injury. Further, we will use pharmacologic and genetic strategies to block and activate CaMKII to examine its role in regulating neuronal electrophysiology. Our SECOND AIM is to determine the effect of CaMKII on the intracellular Ca2+ signal. Despite the central role of Ca2+ in controlling neuronal function, there has been minimal investigation of the influence of nerve injury and associated changes in CaMKII on the critical processes that shape the Ca2+ signal. Accordingly, we will examine Ca2+ management in injured and control rats while altering CaMKII activity pharmacologically and by CaMKII knockdown through siRNA expression. Specific Ca2+ uptake and release pathways will be examined while measuring Ca2+ in subcellular compartments. In our THIRD AIM, the importance of CaMKII regulation of Ca2+ in pain will be directly tested by measuring pain behavior in rats during selective genetic and pharmacologic modulation of CaMKII activity within specific DRGs. Importance to Public Health: This project will provide better understanding of how nerve injury causes chronic pain. This new knowledge may lead to the development of therapies that are delivered selectively to the peripheral nerve, in order to correct abnormal Ca2+ signaling and thereby relieve nerve injury pain.